1. Field of the Invention
This invention relates to a semiconductor photoelectric conversion device employing a semiconductor layer having at least one inter-semiconductor heterojunction, and it also pertains to a method of making such a semiconductor photoelectric conversion device.
2. Description of the Prior Art
Heretofore, there have been proposed a variety of photoelectric conversion devices which employ a semiconductor layer having at least one inter-semiconductor heterojunction.
Typical photoelectric conversion devices are a p-n or n-p type photodiode having one p-n heterojunction, a p-i-n or n-i-p type photodiode having one p-i heterojunction and one n-i heterojunction, a p-i-i-n or n-i-i-p type photocell having one p-i heterojunction, one i-i heterojunction and one n-i heterojunction, a p-n-p-n or n-p-n-p type photocell having three p-n heterojunctions, a p-i-n-i-p-i-n type photocell having two p-i heterojunctions and three n-i heterojunctions.
These semiconductor photoelectric conversion devices are of the type that make effective use of a difference in height between a barrier against electrons injected from one of two semiconductor regions into the other across a heterojunction defined therebetween and a barrier against holes injected from the latter to the former.
The conventional photoelectric conversion devices are all made of a single crystal semiconductor. There is a certain limit to mass production of single crystal semiconductors in terms of manufacturing techniques and economy; this imposes certain limitations on mass production of the semiconductor photoelectric conversion devices.
Further, the semiconductor photoelectric conversion devices made of single crystal semiconductor have abrupt heterojunctions, each formed between two single crystal semiconductor regions having different energy gaps. Since there is a difference in lattice constant between the two single-crystal semiconductor regions having defined therebetween the abrupt heterojunction, dangling bonds are formed locally at the position of the heterojunction, and consequently interface states or defects are present locally at the position of the heterojunction, resulting in an energy band structure that has, at the position of the heterojunction, an energy spike or notch extending towards either one of a valence band or a conduction band.
Accordingly, in the conventional photoelectric conversion devices, during operation electrons or holes to be injected from one of the two semiconductor regions into the other across the heterojunction are partly absorbed by the interface states or defects appearing at the position of the heterojunction, and migration of electrons or holes from one of the two semiconductor regions to the other across the heterojunction is limited by the energy spike or notch at the position of the heterojunction; therefore, there is a certain limit to obtaining high photoelectric conversion efficiency in the prior art.